Optical communication networks conventionally use wavelength division multiplexing (WDM) technology to increase the bandwidth being carried by the network. As is well known, such WDM technology generally includes transmitting a plurality of distinct wavelengths each of which carries data. These wavelength channels are optically combined and transmitted over an optical fiber to a receiver where they may be demultiplexed into separate wavelengths that may be detected to recover the data.
In recent years, the number of wavelengths (channel count) has increased dramatically.
Furthermore, typical optical networks are now quite dynamic in that various wavelength channels may be added, dropped, or selectively switched at various points in the network. Such dynamic networks have a need for channel filters, particularly dynamic channel filters than can selectively transmit or block certain wavelength channels upon command.
This need has driven the invention of so-called reconfigurable blocking filters (RBFs) such as those described in U.S. Pat. Nos. 6,141,361; 5,974,207; 5,960,133. Such dynamic channel filtering can also be accomplished with so-called optical router technology as described in, for example, U.S. Pat. Nos. 6,625,346 and 6,687,431.
A typical application of such reconfigurable blocking filters and optical routers is within an optical add/drop multiplexer (OADM) in which the RBF or wavelength router is placed along the express path of the OADM so as to selectively pass or block certain channels. Channels are typically blocked along the express path of an OADM in order to permit the insertion of wavelength channels having the same wavelength. More specifically, wavelength channels are typically dropped at an optical node which leaves that bandwidth available for the insertion of other data at the same wavelength.